Leak detection system

ABSTRACT

A surgical device includes a device body defining a sealed fluid path having a first end and a second end, a refrigerant supply in communication with the first end of the sealed fluid path; and a vacuum source in communication with the second end of the sealed fluid path. Leak detection apparatus can be provided in communication with the sealed fluid path.

This application is a divisional of U.S. patent application Ser. No.09/489,707, filed Jan. 24, 2000 U.S. Pat. No. 6,569,158, which claimspriority from U.S. Provisional Patent Application Serial No. 60/117,175,filed Jan. 25, 1999.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

FIELD OF THE INVENTION

The invention relates to medical devices, and more particularly tominimally invasive surgical systems.

BACKGROUND OF THE INVENTION

Medical devices configured for minimally invasive surgery are rapidlybecoming the tools of choice for many surgical procedures. Not only dothese devices provide an alternative-to more invasive surgical tools andprocedures, but they have also fostered the development of entirely newprocedures.

Devices including highly flexible catheters, as well as rigid andsemi-flexible probes have received increased attention in recent yearsand continue to be refined for cardiovascular, pulmonary, urogenital,and other applications. Devices for each of these applications presentdifferent technology and material challenges. Angioplasty catheters, forexample, can require fluid-tight passages or channels for circulating acooling fluid (liquid or gas) through a catheter to cool anelectro-surgical structure, such as radio frequency ablation electrode,to prevent overheating of the electrode or of surrounding tissue.Similarly, a cooling or cryogenic fluid can be reduce the temperature ofa structure, such as an ablation surface, to a therapeutic temperature.Some cooling fluids, however, can be harmful or fatal to the patient ifthey unintentionally escape from the surgical device.

Although careful fabrication techniques, quality materials, and thoroughtesting can reduce the chances of cooling fluid leakage, it would bedesirable to provide additional system features that further minimizethe occurrence of leaks; and should a leak occur, provide features thatdetect cooling fluid loss or escape immediately so that use of thesurgical device can be terminated and patient remediation efforts can beundertaken if required.

SUMMARY OF THE INVENTION

The present invention provides an improved surgical device including adevice body defining a sealed fluid path having a first end and a secondend, a refrigerant supply in communication with the first end of thesealed fluid path, and a vacuum source in communication with the secondend of the sealed fluid path. Leak detection apparatus can be providedin communication with the sealed fluid path.

Exemplary leak detection apparatus include an impedance measurementcircuit, an infrared sensor, and a pulsed ultrasonic device. A controlunit that is in communication with the leak detection apparatus isresponsive to output from the leak detection apparatus to control fluidflow through the sealed fluid flow path.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic view of a minimally invasive surgical systemincluding a leak detection system in accordance with the invention;

FIG. 2 illustrates an exemplary cryocatheter tip with a leak detectioncircuit;

FIG. 3 illustrates a porous, insulated, conductive wire within acryocatheter tip; and

FIG. 4 illustrates another leak detection device.

DETAILED DESCRIPTION OF THE INVENTION

In the discussion which follows, “surgical device” is intended toencompass any surgical implement used in association with human oranimal medical treatment, diagnosis, study, or analysis. Moreparticularly, a surgical device is intended to encompass any implementor portion thereof that is entirely or partially inserted into a humanor animal body by any means of entry, such as through a natural bodyorifice, an incision, or a puncture. The term surgical device is notintended to connote a limitation to treatment of a single body system,organ, or site. The surgical device can be rigid as a thick steel pipe,completely flexible and pliant like a thread, or have a flexibilitybetween the two extremes. The surgical device can have a diameter thatranges from inches to microns.

As used herein, “fluid” is intended to encompass materials in a liquidstate, a gas state, or in a transition state between liquid and gas, andliquid and solid. The fluid can be a “cryogenic fluid” capable ofreaching or creating extremely cold temperatures well below the freezingpoint of water, such as below minus 20 degrees Centigrade; a “coolingfluid” that does not reach or create temperatures below the freezingpoint of water; a fluid capable of transferring heat away from arelatively warmer structure or body tissue; a fluid capable oftransferring heat to a relatively cooler structure or body tissue; afluid at or capable of creating a temperature between the freezing andboiling points of water; and a fluid at or capable of reaching orcreating a temperature above the boiling point of water.

A “fluid path” as used herein is intended to encompass any boundary,channel or guide through which a fluid can travel. It can includeconcentrically disposed catheters, multi-lumen catheters, or a singleloop of tubing within a sheath. The fluid path can also includeconnectors and valves, as well as passages in support equipment, such asthe console disclosed herein.

Referring now to FIG. 1, an exemplary surgical device is illustrated forminimally invasive surgery. The surgical device includes a console 10and a multi-lumen catheter 12. The console 10 houses electronics andsoftware for controlling and recording a surgical procedure, such asablation, and it controls delivery of liquid refrigerant under highpressure from a supply container 13, through an umbilical 14, to thecatheter 12. A second umbilical 16 is provided for transferringrefrigerant from the catheter 12 to console 10. The console 10 isprovided with apparatus 15 for recovery of expanded refrigerant vaporfrom the catheter and recompression of the vapor.

Either or both of the catheter 12 and the console 10 can be providedwith detection devices that are in electrical communication with theconsole and which provide a signal output that can be representative ofan event that indicates flow path integrity loss or a leak within asealed catheter and/or console. As shown in FIG. 1, a first detectiondevice or leak detector 18 can be provided in a body or tip portion ofthe catheter 12. A second leak detector 20 can be provided in the handleportion 21 of the catheter 12; and a third leak detector 22 can beprovided in the console 10. The console 10 can be configured to respondto signal output from the leak detectors and initiate a predeterminedsequence of events, such as discontinuing refrigerant injection,changing the pressure within the system, and controlling removal ofrefrigerant from the catheter 12.

The purpose and function of the leak detectors is better understood onceanother feature of the invention is introduced, namely, a vacuum pump24, as shown in FIG. 1 in fluid communication with a catheter 12. Thethird leak detector 22 can be interposed between the vacuum pump 24 andthe catheter 16. The vacuum pump 24 is controllable to reduce thepressure within the return lumen of the catheter 12 and the secondumbilical 16 to provide a pressure ranging from a pure vacuum to apressure just below a patient's blood pressure. For example, the vacuumcan maintain a selected pressure between 80 mm Hg and 0 mm Hg. Theprovision of reduced pressure within the return flow path of thecatheter significantly enhances patient safety because, should a leakoccur, refrigerant will not squirt from the leak into the patient.Rather, bodily fluids in the treatment site will be aspirated into thecatheter whereupon they are sensed by one or more of the leak detectors.In one mode of operation, when a leak is detected, the refrigerantinjection is turned off automatically and vacuum is kept on to ensurethat no refrigerant enters the patient's body.

Although a single type of leak detector could be functional, anexemplary embodiment of the invention is provided with three differenttypes of leak detectors for enhanced detection probability. For example,the first leak detector 18 can be a simple circuit formed by a wire,such as a pull-wire used to help steer the catheter tip, and aconductive catheter tip portion. Specifically, as shown in FIG. 2, awire 26 is electrically isolated from a metal catheter tip 28 and metalelectrode rings 29. In the illustrated embodiment, the wire is securedto a non-conductive support element 30. Also shown is a refrigerantinjection tube 32. The electrical impedance between the wire 26 and thecatheter tip 28 is monitored. If a liquid enters the catheter 12 andtouches the wire 26 and the tip 28, a short is created which isdetectable by circuitry in the console. Alternatively, the wire 26 andone or more of the electrode rings 29 can be included in the impedancecircuit.

However, some catheters 12 may include multiple conductors runningwithin one or more lumens and electrical insulation on the conductors isnecessary to avoid unwanted electrical connections and interferences.Many such catheters also contain uninsulated wires, for example asmechanical deflectors to alter catheter configuration, or for example asstiffening agents to alter catheter flexibility or pushability. However,if the pull wire (or other wire that is part of the leak detectioncircuit) contacts another uninsulated wire, electrode ring or otherconductive element, a false leak detection signal could be generated.Accordingly, a form of insulation that provides mechanical insulationwhile allowing fluid conductivity is desirable.

FIG. 3 discloses a wire 34 (such as a pull wire) that is part of theleak detection circuit. The wire 34 is covered with a porous material36, such as a fabric, salt-depleted polymer, or laser drilled polymer,that provides mechanical insulation in the dry state by the physicalbulk and separation of the porous material, which allows passage ofionic fluids to the thus insulated wire to complete the electrical leakdetection circuit.

Although the first leak detector 18 is well suited for detecting leaksat or near the distal end of the catheter 12, a leak may develop betweenthe distal end and the handle portion 21 of the catheter and an infraredsensor can be disposed in the handle as the second leak detector 20. Assoon as the first and/or second leak detectors output a signal to theconsole indicative of a leak, the refrigerant injection can be stopped.In an exemplary embodiment, shown in FIG. 4, an infrared sensor 38 witha wavelength sensitive to blood composition is disposed in sensing rangewith a transparent window 40 or tube along or forming part of the returnfluid flow path 42.

Even though refrigerant injection is stopped, it can still be desirableto apply vacuum to the catheter to withdraw refrigerant alreadyintroduced into the catheter, along with refrigerant contaminated blood.Thus, a third leak detector 22 (shown in FIG. 1) is provided furtherdownstream in the fluid flow path to not only provide a last opportunityfor detection, but to also detect when a selected volume of blood hasbeen aspirated (a relatively small amount) and to then terminate vacuumoperation or aspiration. Depending on placement of the third leakdetector, it can prevent blood contamination of the entire fluid flowpath within the console 10.

Although the invention has been shown with respect to exemplaryembodiments thereof, various other changes, omissions and additions inform and detail thereof may be made therein without departing from thespirit and scope of the invention.

What is claimed is:
 1. A surgical device comprising: a device bodydefining a sealed fluid path having a first end and a second end; asupply of a cryogenic fluid in communication with the first end of thesealed fluid path; a vacuum source in communication with the second endof the sealed fluid path; a leak detection apparatus in direct fluidcontact with the sealed fluid path, said leak detection apparatus havingat least a portion of an impedance measurement circuit in the sealedfluid path, said impedance measurement circuit including a conductiveportion of the device body and a wire disposed within the device body,the wire being electrically isolated from the conductive portion of thedevice body, and a fluid porous coating disposed around a portion of thewire.
 2. The surgical device of claim 1, wherein the fluid porouscoating includes a fabric.
 3. The surgical device of claim 1, whereinthe fluid porous coating includes a salt-depleted polymer.
 4. Thesurgical device of claim 1, wherein the fluid porous coating includes alaser-drilled polymer.
 5. The surgical device of claim 1, furthercomprising a control unit that is in communication with the leakdetection apparatus, wherein the control unit is responsive to outputfrom the leak detection apparatus to control fluid flow through sealedfluid path.
 6. The surgical device of claim 1, wherein the device bodyincludes a catheter and the refrigerant cryogenic fluid is capable ofreducing the temperature within a portion of the catheter to atemperature below minus 20 degrees Centigrade.
 7. A surgical devicecomprising: a catheter having proximal and distal end portions, andhaving a sealed flow lumen, the flow lumen having first and second endportions; a supply of a cryogenic fluid in communication with the firstend portion of the flow lumen; a vacuum source in communication with thesecond end portion of the flow lumen; an impedance measurement circuitdisposed inside the flow lumen, including a first conductive elementdisposed on the distal end portion of the catheter, and a secondconductive element disposed within the sealed flow lumen, the firstconductive element being electrically isolated from the secondconductive element.
 8. The surgical device of claim 7, wherein the firstconductive element is a metal catheter tip.
 9. The surgical device ofclaim 7, wherein the second conductive element is a metal wire.
 10. Thesurgical device of claim 7, further comprising a fluid-permeableinsulation element disposed around the second conductive element. 11.The surgical device of claim 10, wherein the second conductive elementis a metal wire.
 12. The surgical device of claim 10, wherein thefluid-permeable insulation element is porous to allow passage of ionicfluids.
 13. The surgical device of claim 10, wherein the fluid-permeableinsulation element is a fabric.
 14. The surgical device of claim 10,wherein the fluid-permeable insulation element is a salt-depletedpolymer.
 15. The surgical device of claim 10, wherein thefluid-permeable insulation element is a laser-drilled polymer.